Jungle Research Group
at the Atmospheric Sciences Research Center

Large-Scale Biosphere-Atmosphere Experiment in Amazonia

    This study presents the results of a changing land use in an agricultural field in eastern Amazon.  A major focus will be to determine how carbon fluxes are influenced by natural and human-induced landscape inhomogeneities.   Fluxes will also be estimated using the boundary layer budget approach.  Scales of inhomogeneities addressed range from the river-land contrast, the pasture-forest contrast, and the gap-closed canopy contrast inside the forest.  Special attention will go to understanding how changes in agricultural practices in the Amazon alter carbon exchanges in cleared areas.  One new initiative aims to improve understanding of the respiration rate in forests by studying subcanopy flows.  A second initiative to quantify canopy structure to relate this structure to the forest flux tower observations is proposed.

Our Objectives are:

    1) To observe local wind circulations (river and land breezes, drainage flows) and assess their influence on boundary layer development.  To infer surface heat, water vapor, and CO₂ fluxes from temporal changes in their canopy and boundary layer concentrations.

    2) To relate light availability to the ecosystem to cloudiness, and to determine the resulting effect on net ecosystem carbon exchange (NEE).

    4) To quantify the vertical and horizontal structure of the forest canopy near flux towers in the Tapajos National Forest.

    6) To reduce uncertainties in long-term tower flux observations of the respiration rate through better understanding the effect of subcanopy drainage flows at two LBA-ECO Study Areas.

At site km 77, a 20 m micrometeorological tower was installed to measure turbulent fluxes (momentum, heat, water vapor, and CO₂) using the eddy covariance approach (EC), soil heat flux, wind and scalar profiles (T, q, and CO₂), soil moisture content, terrestrial, total solar radiation, and PAR (photosynthetically active radiation).  At the beginning of the measurements, in September 2001, the field was a pasture.  On November 2001, the field was burnt, plowed and upland rice was planted. 

Land use change affects not only turbulent exchanges but also the phenology of the site.  Greenness of the vegetation is clearly detected from the albedo and PAR-albedo, including seasonal differences such as wet and dry periods.  These changes alter the net radiation over the site, and thus the heat transfer and evaporation regime, different from the nearby forest that the net radiation depends solely on the cloudiness. The highest evaporation rate observed is over the rice crop, where the field has an evapotranspiration of about half of the precipitation input.  However, the evapotranspiration is less intense than the surrouding forest.  Changes of the land use are also detected in the carbon budget.  For the pasture, the maximum pasture CO₂ uptake occurs in May, appreciably delayed from the start of the rainy season.  After the field was cleaned and the soil was exposed and there was an efflux of CO₂ to the atmosphere.  Highest values of carbon uptake occurred during the rice plantation.  Though the upland rice takes up carbon at double the rate of the pasture that it replaced, the field was left fallow for much of the year, during the dry season.  Thus changes from pasture to a crop field are going fully assessed when the secondary growth of the rice will be analyzed.  According to biometric and to the NEE results, this agricultural field is more efficient to sequester carbon.

LBA Sites:     

Links:

LBA Project Sites

LBA Images

LBA 2002 Final Proposal

CD-03 Progress Report

Pasture 2001 Presentation

LBA-Mexico Powerpoint Presentation

Report by Geoffrey G. Parker, Smithsonian Environmental Research Center

Atmospheric Sciences Research Center:  Jungle Research Group